The following abbreviations are used throughout this document:
ACH Associated Channel Header
CC Continuity Check
CFM Connectivity Fault Management
CV Connection Verification
IW Interworking
LBM Loopback message
LBR Loopback reply
LSR Label Switching Router
LSP Label Switched Path
LTM Linktrace message
LTR Linktrace reply
MA Maintenance Association
MAC address Media Access Control address
MEP Maintenance Association End Point
MIP Maintenance Domain Intermediate Point
MPLS Multiple Protocol Label Switching
MPLS-TP MPLS Transport Profile
OAM Operation, Administration and Maintenance
PW Pseudo Wire
TLV Type Length Value
TTL Time To Live
In communication systems Loopback is generally used to describe methods or procedures for routing electronic signals, digital data streams, or other flows of items, from their originating facility quickly back to the same source entity without intentional processing or modification. Loopback is primarily intended as a means of testing the transmission or transportation infrastructure. In general, the routing of signal is initiated at a maintenance node, transmitted to a target node and back again to the maintenance node.
Examples of Loopback applications include e.g. performing transmission tests of access lines from a serving switching center (i.e. from the maintenance node), which usually does not require the assistance of personnel at the served terminal (i.e. at the target node). Loopback is often used as an aid in debugging physical connection problems between various nodes.
In the same communication systems so called Linktrace is often also performed, which describes methods or procedures that perform path discovery and fault isolation, which includes a possibility to map the topology of the communication system. Both Linktrace and Loopback as well as other, similar functionality such as continuity check (CC) are often grouped under and referred to as connectivity fault functions within the operation and maintenance (OAM) group of functions which usually contains performance monitoring functions as well.
In some communication systems different types of network technologies are combined, for example when an Ethernet network is combined with a network implemented according with technology for a Multiple Protocol Label Switching (MPLS) network. Performing OAM operations can in this case be more challenging since the functionality must enable cooperation (i.e. interwork) between the different types of networks. In a more general perspective, using a node in the Ethernet network for finding a node in the MPLS network or using a node in the MPLS network for finding a node in the Ethernet network can be troublesome.
As an example of prior art, US2008/0144657 describes an apparatus for realizing OAM function interworking between an Ethernet network and an MPLS network. The apparatus can realize OAM functions when MPLS serves as a bearer network to bear Ethernet services, and provides processing modes for different kinds of OAM functions. Based on the Ethernet-MPLS service interworking function model defined in ITU-T Recommendation Y.1415, the embodiments of the apparatus realizes interworking of Ethernet OAM functions defined in ITU-T Draft Recommendation Y.17ethoam and MPLS OAM functions defined in ITU-T Recommendation Y.1711 on network layer, which shall ensure an end-to-end OAM interworking mechanism between Ethernet and MPLS networks.
Even though exemplified and other existing techniques can provide some interworking between en Ethernet based network and an MPLS based network, it is appreciated that improvements are required for making interworking more applicable and operator friendly.